When inert foreign bodies such as metals, ceramics, plastics, or the like, are implanted or contacted with living tissue, such as in an animal or the human body, the living tissue builds up a defensive fibrosis around this body in an effort to reject, insulate and isolate it from the vascularized tissue. In the case of electric terminals or electrodes, particularly those for stimulation for heartpacers as described in applicant's U.S. Pat. No. 3,659,615, issued May 2, 1972, its metal electrodes puncture the myocardium and soon become coated with fibrous tissue reducing the electrical conductivity into the muscle.
L. W. Smith et al in their U.S. Pat. No. 3,314,420 issued Apr. 18, 1967 disclosed a porous ceramic material as a bone substitute into which body tissue grows.
F. W. Rhinelander et al in their article entitled "Microvascular and Histogenic Responses To Implantation Of A Porous Ceramic Into Bone" published in J. Biomed. Mater. Res. Vol. 5 pp 81-112 (1971) disclosed that bone tissue containing blood capillaries grew deep into and intermeshed with the porous ceramic materials patented by Smith et al. Furthermore, S. F. Hulbert et al in their article entitled "Compatibility Of Porous Ceramic With Soft Tissue; Application To Tracheal Prothesis" published in J. Biomed. Mater. Res. Symposium Vol. 2 (part 1) pp 267-279 (1971) disclosed that soft tissue containing blood capillaries also grew deep into the interconnecting pores of porous ceramics.
R. B. Beard et al in their article entitled "Porous Cathodes For Implantable Hybrid Cells" published in the I.E.E.E. Transactions on Biomedical Engineering, Vol. 19, No. 3 May 1972, disclosed that porous platinum and palladium black catalystic electrodes for power generation when implanted in soft tissue produced a surrounding tissue capsule having apparent revascularization in said capsule, and that there were some apparent tissue ingrowth into the pores of the electrodes which caused poisoning of its catalystic effect. Furthermore, the formation of a granulated or fibrous tissue around implanted active porous electrodes, such as for fuel cells, was disclosed into the Drake et al article entitled "A Tissue Implantable Fuel Cells Power Supply" published in Vol. XVI Trans. Actions American Soc. Artif. Int. Organs 1970 pp 199-205.
Accordingly, the problem was to produce a non-reacting implantable electric terminal without the formation of a fibrous tissue coating.